1. Field of the Invention
The present invention relates to a variable magnification optical system, for example, a variable magnification optical system suitable for a digital camera and a digital appliance provided with an image input capability that take in an image of a subject by an image sensor (especially a compact zoom lens system that offers high magnification variation ratios), and to an image-taking apparatus provided with such as a variable magnification optical system.
2. Description of Related Art
In recent years, as personal computers become increasingly widespread, digital cameras which permit easy acquisition of images have been becoming more and more popular. Consequently, there has been a demand for a more compact, thinner digital camera, which leads to a demand for an even more compact image-taking lens system. Due to the yearly increasing trend of the number of pixels included in the image sensor, the image-taking lens system has been required to offer high optical performance so as to catch up with the increase in the number of pixels included in the image sensor. Even in digital cameras designed for general consumers, magnification variation of an image, optical magnification variation with little image degradation in particular, is sought. Thus, in order to meet the demand for downsizing with higher performance and higher magnification variation ratios, various types of conventional zoom lens systems have been suggested (see Patent document 1, for example).                [Patent Document 1] Japanese Patent Application Laid-open No. 2004-170707        
However, the suggested conventional zoom lens systems have difficulty in meeting the mutually contradictory demands for downsizing with higher performance and higher magnification variation ratio. For example, in the conventional zoom lens system suggested in the patent document 1, an optical path is bent twice so as to provide a zoom ratio of about 5 or more while suppressing the height and width of the camera. Considering the balance with the optical performance, however, the zoom lens system is not sufficiently downsized.